Polytetramethylene ether glycol (PTMEG) is a high volume commercial product. PTMEG having a number molecular weight of from 600 to 2,200 is widely used in the formation of block copolymers used as soft (elastomeric) segments in polyurethanes or polyesters such as polytetramethylene terephthalate. The block copolymers with polyurethanes are widely used to form the spandex fibers often found in stretch textile fabrics. The block copolymers with polyesters are used to form injection moldable elastomers having a wide variety of uses, often industrial or automotive.
The ring opening of tetrahydrofuran using dry trifluoromethane sulfonic acid (triflic acid) to form polymers having molecular weights in excess of 10,000 has been reported. However, the commercial grades of PTMEG range in number molecular weight from 600 to 2,200. Consequently dry triflic acid has never been considered a suitable candidate for making PTMEG on a commercial scale.
PTMEG is generally made commercially by polymerizing tetrahydrofuran (THF) using fluorosulfonic acid as the catalyst. In the reaction the sulfate ester of PTMEG is formed which is hydrolyzed to produced PTMEG and sulfuric and hydrofluric acids. About 95-98 wt % of these acids are washed out of the product with water. The residual quantity of acids in the finished product is neutralized with calcium hydroxide. The solids are then filtered, the product dried and sent to a storage tank. This existing process suffers from a number of disadvantages. First, the fluorosulfonic acid, used as the commercial catalyst, is not recoverable because it participates in the reaction and represents an expensive loss. Second, large quantities of acids have to be neutralized which is expensive and the product is undesirable from an environmental point of view because of its toxicity and corrosiveness. Third, the filtration produces a very substantial yield loss and operating expense.